Closure bag with internal tack surfaces

ABSTRACT

A closure bag having a bag body with internal tack surfaces.

This is a division of application Ser. No. 08/554,945, filed Nov. 13.1995, now Pat. No. 5,965,224 entitled "CLOSURE BAG WITH INTERNAL TACKSURFACES"

FIELD OF THE INVENTION

The instant invention relates to a closure bag having sidewalls withinner surfaces with unique internal "tack" characteristics such thatresidual air in the bag can be expelled after food or other article isplaced in the bag prior to closing the closure by pressing the internalsurfaces together such that the surfaces adhere to each other.

BACKGROUND OF THE INVENTION

The use of closure fastening devices for the closure of containers,including plastic bag bodies, is generally known. Furthermore, themanufacture of closure fastening devices (commonly referred to as"closures") comprising adhesive closures or interlocking zipper closuresformed from plastic materials is generally known to those skilled in theart relating to closure fastening devices as demonstrated by thenumerous patents in this area.

Adhesive closures for bags are disclosed in representative U.S. Pat.Nos: 4,519,095, 4,415,087 and 3,990,627.

Zippers of the type used on plastic bags are well known. Patents whichdisclose "zippers" and zippers on bags include U.S. Pat. No. 4,186,786,and U.S. Pat. No. 4,285,105, Japanese Patent Application No. 51-27719.

A search of the prior art located the following patents:

U.S. PATENTS

3,160,323

3,198,392

3,260,412

3,353,714

3,504,067

4,518,654

4,842,421

4,963,388

5,049,423

5,147,708

The above prior art relates to containers having internal surfaces withmechanical mating (see: U.S. Pat. Nos. 3,198,392, 3,260,412 and3,160,323) or tube scoring (see: U.S. Pat. Nos. 3,353,714 and 3,504,067)and to so called cling stretch wraps (see: U.S. Pat. Nos. 4,518,654,4,963,388, 5,049,423 and 5,147,708). U.S. Pat. No. 4,842,421 relates toa thermoplastic draw tape bag having a tacky surface around the innerperiphery of the lip of the open mouth of the bag.

A particularly well-known closure fastening devices is in connectionwith a flexible container, e.g., bag bodies and are generally referredto as zippers. The closure fastening device and the associated containermay be formed from thermoplastic materials, and the closure fasteningdevice and sidewalls of the container can be integrally formed byextrusion as a single piece, or may be formed as separate pieces andthen connected by heat sealing or other suitable fastening means.

SUMMARY OF THE INVENTION

The instant invention generally relates to a plastic bag having aclosure and a bag body having opposing sidewalls with the inner surfacesof the bag body having at least one tack surface area whereby the twoinner surfaces adhere to each other when the surfaces come into physicalcontact. This adhesive between the inner bag surfaces enables removableof residual air prior to closing the bag's closure. The removal ofresidual air is generally believed to be beneficial to improved foodstorage conditions.

DESCRIPTION OF THE DRAWING

FIG. 1 is a bag having a closure with inner surfaces and outer surfaces.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention provides a closure bag with means for removingresidual air in a bag prior to closure. This is accomplished without theneed for additional venting means for forcing air from a closed bag.

The terms "inside" and "outside" are employed herein to refer to thesurfaces of the sidewalls of the bag body with the "inside" referring tothe side of the sidewall coming into contact with the article placedwithin the bag.

The "inside" surfaces or "inner" surfaces of the bag body are providedwith a unique "tack" characteristic not heretofore employed with closurebags. This "tack" characteristic is provided to facilitate the removalof residual air in an open bag into which an article has been placed.The user of the bag presses the sidewalls on the outside surfaces sothat the inside surfaces are in physical contact. As a result of the"tack" characteristic of the two inner surfaces for each other the twosurfaces adhere to one another and expel any residual air which wouldotherwise have remained between spaced apart sidewalls of the bagbodies.

The "tack" characteristic of the inside surfaces of the bag body can beprovided by several means with varying levels of "tack" resulting fromthe selected means of providing the "tack" characteristic. In oneembodiment the bag body is formed from a multilayer film having theinside surface formed from a film layer containing a tackifying agentassociated with at least a portion of at least one of the two insidesurfaces. Tackifying agents include glycerol monooleate, amorphouspolypropylene, amorphous polypropylene-ethylene copolymer,polyisobutylene (copolymers of isobutylene and butene), terpene resins,alkali metal stearates, hydrogenated rosins, rosin esters, pressureactivated adhesives and the like. One or more of the aforementionedtackifying agents can be blended with resin materials to be extruded asa film layer of a multilayer film or as a single film layer, such resinmaterials including, low density polyethylenes, linear low densitypolyethylenes, high density polyethylenes, polypropylenes, ultra lowdensity polyethylenes, amorphous polyethylenes, ethylene vinyl acetates,polyamides, polyesters and mixtures thereof. If the multilayer film hasthree or more layers the internal layers can be selected to providemoisture barrier or air barrier or other beneficial properties and caninclude one or more of the above materials and other thermoplastics suchas ethylene vinyl alcohol copolymers. Since a bag sidewall formed from asingle layer containing one or more tackifying additives will have boththe inside and outside surfaces of the bag body with a "tack"characteristic the outside surface in such an embodiment wouldpreferably be treated with a process or chemical to reduce the tackcharacteristic of the outside surface. For example, the outside surfacecan be treated with an effective amount antiblock agent to reduce the"amount of" tackiness of a surface. This treatment may be provided byincreasing the amount of antiblocking agent added to the resin prior toextrusion. Antiblocking agents useful for this treatment includesilicas, talc and the like. Alternatively, a chemical treatment can beprovided to the outside surface. Such a chemical treatment would includecorona discharge treatment, coating or printing (e.g., with an ink) witha continuous or non-continuous chemical or reducing the tackiness of theoutside surface by reaction with other chemical reactants. Althoughtreatment of the outside surface is not required, users of a quantity ofthe bags seeking to remove a bag from dispensing box will find itbeneficial to have a reduced tackiness associated with the outsidesurface of the bag body.

When the bag sidewalls are a multilayer film the outer layer may beformed from thermoplastic materials such as low density polyethylenes,high density polyethylenes, ultra low density polyethylenes,polypropylenes, polyamides, polyesters, or the like or from acombination thereof. The selection of the outer film material should besuch that it doesn't interfere with the inner surfaces of the bag body.Further, mixtures of resins such as high density polyethylene, mediumdensity polyethylene, low density polyethylene, low densitypolyethylene, linear low density polyethylene and ethylene vinyl acetatemay be employed.

The closure of the closure bag may be any closing means appropriate forclosing the bag. Well known closing means are zipper type closures andadhesive type closures. Representative of zipper type closures are U.S.Pat. Nos: 3,654,049; 4,186,786; 4,212,337; 4,285,105; 4,295,919;4,372,014; 4,561,108; 4,561,109; 3,578,813; 4,829,641; 4,907,321; Re.28,969; 3,338,284; 3,565,147; 4,362,198; 4,484,352; 4,516,268;5,252,281; 5,138,750; 5,140,727; 5,070,584; European Patent ApplicationNo. 510,797 (published Oct. 28, 1992); 4,929,487; 4,858,286; 4,363,345;5,198,055 and 5,356,222, incorporated herein by reference thereto.Representative of adhesive type closures are U.S. Pat. Nos: 4,519,095;4,415,087; 3,990,627; 3,942,713; 3,085,738; 3,670,876; 3,806,024;4,410,130; 4,502,599; 4,785,940; 4,842,421; 4,902,142; 4,947,525 and5,078,509, incorporated herein by reference thereto. The actual closuremeans is selected to provide a bag which is suitable for the intendeduse. If the bag is intended for use as a food storage bag the closuremeans should be as close to "air tight" as possible to minimize airintroduction into the bag from the atmosphere outside the bag.Accordingly, a zipper type closure is typically selected owing to theability of zippers to keep substantially all of the air out of the bagafter closure and owing to their ability to be repeatedly reopened andclosed.

In practice, zipper bags are formed such that the zipper is integrallyformed with the sidewalls of the bag, or connected to a container, bythe use of any of many known methods. A thermoelectric device can beapplied to a film in contact with a flange portion of a zipper or thethermoelectric device can be applied to a film in contact with the baseportion of a zipper having no flange portion, to cause a transfer ofheat through the film to produce melting at the interface of the filmand the flange portion or base portion of the zipper. The bonding of thezipper to the film stock may be carried out either before or after thefilm is U-folded but in any event is done prior to side sealing the bagsat the edges by conventional thermal cutting. The thermoelectric devicecan be heated rotary discs, or resistance heated slide wires, ortraveling heater bands, or the like. The connection between the film andthe zipper can also be established by the use of hot melt adhesives, orhot jets of air to the interface, or ultrasonic heating, or other knownmethods.

Generally, the zipper and the films that form the body (having opposingsidewalls) of the bag can be made from a heat sealable material so thata container can be formed economically by heat sealing theaforementioned components to form the container using thermoplastics ofthe type aforementioned for formation of the closure elements. Thetypical thickness of a bag sidewall is well known in the art and istypically between about 0.5 mil and about 5 mils and more typicallybetween about 1 mil and 3 mils.

Generally, the closure fastening device of this invention can bemanufactured in a variety of forms to suit the intended use. Inaddition, the two closure elements of the zipper can be positioned onopposite sides of a film.

In evaluating the instant invention a series of closure bags wereprepared using the following resin materials and tackifying additives:

Resins:

Low Density Polyethylene ("LDPE")

High Density Polyethylene ("HDPE")

Linear Low Density Polyethylene ("LLDPE")

Tackifying Additives:

Polyisobutylene ("PIB")

Ethylene Vinyl Acetate ("EVA")

Six (6) two layer bag films were made having the following inside filmand outside film by coextruding the two layer film on a slot castingextrusion line and having a thickness of 3.0 mils with the thicknessratio of the inside film layer to outside film layer being about 1.

The six films were:

Film 1:

Inside Film: 87.4 wt % LDPE, 7.6 wt % HDPE and 5 wt % PIB.

Outside Film: LDPE with 5000 ppm fine silica antiblocking additive.

Film 2:

Inside Film: 87.4 wt % LDPE, 7.6 wt % LLDPE and 5 wt % of PIB.

Outside Film: Same as for Film 1.

Film 3:

Inside Film: 95 wt % LDPE and 5 wt % PIB.

Outside Film: Same as for Film 1.

Film 4:

Inside Film: 95 wt % LLDPE and 5 wt % PIB.

Outside Film: Same as for Film 1.

Film 5:

Inside Film: EVA

Outside Film: 30 wt % HDPE, 30 wt % LDPE and 40 wt % LLDPE.

Film 6:

Inside Film: 94 wt % EVA and 6 wt % PIB.

Outside Film: 30 wt % LDPE and 70 wt % LLDPE.

Each of the above films were formed into zipper bags of the type shownin FIG. 1 where the inside of the bag had sidewalls with opposing insidefilms. The zipper was of the type claimed in U.S. Pat. Nos. 4,829,641and 4,907,321, incorporated herein by reference thereto. The bags weretested by placing an eight ounce steak in an open bag and pressing theinside surfaces into contact to expel residual air from the internalarea of the bag not occupied by the steak. Each of the bags tested wasobserved to provide the internal tack characteristic of the instantinvention wherein the inside surfaces of the bag body adhered to eachother upon coming into physical contact. The magnitude of the adherencevaried as among the six different films with film 6 providing a veryhigh adhesion between the inner surfaces with film 2 providing a lesseradhesive force but being preferred owing to ease of use.

Referring to FIG. 1, a closure bag 10 is shown having a first sidewall12 and a second sidewall 14, each sidewall having an inside surface andan outside surface with inside surface 12a of first sidewall 12 shownand outside surface 14a of second sidewall 14 shown. Closure bag 10 isformed with side seals at 16, 18 and 20 to form a bag body with aclosure means having closure element 22 and 24. According to thisinvention the inner surface of at least one sidewall 12 (shown as 12a)and 14 (not shown) has a tacky surface such that when placed intophysical contact the surfaces stick to one another.

What is claimed is:
 1. A method for using a storage bag for an articleto decrease residual air in said bag comprising:1) selecting a plasticclosure bag comprising a closure in an open position and having twosidewalls, each sidewall having an inner surface and an outer surface,said inner surfaces being arranged to permit physical contact andcharacterized as adhesively adhering when placed in physical contact; 2)placing an article in the bag; 3) pressing said inner surfaces of saidwall into physical contact whereby said sidewalls adhere so as to removeair otherwise between said inner surfaces of said sidewalls; and 4)closing said closure.
 2. A method according to claim 1 wherein saidarticle is food.